Posted by Bill Baer on Saturday, March 14, 2009 at 11:22 am

In one of our divergent conversations on Pro Baseball Central on March 4, I argued with hosts Steve Keane and Joe McDonald that Brad Lidge’s perfect season last year puts him on a track where he can start to be compared to Mariano Rivera. They were, of course, flabbergasted at such a wacky thought. They said that it was as crazy as comparing Billy Wagner to Rivera.

I didn’t really give it much thought until today, just randomly remembering that part of the show. Billy Wagner was pretty freakin’ good — nearly as good as Rivera according to the statistics.

Here’s a quick and dirty comparison of their career totals:

Apologies for the image quality. Microsoft Paint ain’t so great.

Rivera has pitched more innings with about a 10-point lower ERA in a tougher league. Wagner’s got the strikeouts and has allowed a smidge fewer base runners than Rivera.

All told, believe it or not, they have had an eerily similar career path.

Both came into the Majors in 1995, but both weren’t featured as relievers until ‘96. Wagner got a cup-a-Joe in ‘95 and Rivera actually made 10 starts along with 9 relief appearances.

Using this ERA graph from FanGraphs, we can see the similarities from ‘96 moving forward. Click the graph to enlarge it.

Rivera’s only subpar season was his rookie year; Wagner’s was an injury-plagued 2000. Also note that Wagner’s ‘95 season was all of one-third of an inning, so don’t worry about that.

The standard deviation for Rivera and Wagner’s seasons using ERA+ was 59. Only in five of the 13 seasons between 1996-2008 did Rivera have an ERA+ advantage of one standard deviation or greater over Wagner. Those years were 1996-98 (avg. advantage of 86), 2000 (+89), and 2008 (+134).

Where Rivera really has the advantage over Wagner is in the post-season. Wagner has only been there in five seasons; Rivera’s been there every year of his career except ‘08. Overall, Rivera has a 0.77 post-season ERA, including a 0.38 in the ALDS, 0.93 in the NLCS, and 1.16 in the World Series.

Wagner, meanwhile, has an overall 8.71 post-season ERA including a 5.87 ERA in the NLDS, which his team has failed to get past in four of his five appearances. Only in 2006 with the Mets did Wagner reach the NLCS.

But making the post-season is largely out of one player’s control. With regard to the regular season, both players’ 14-year careers have followed a similar arc and the difference in ERA+ between the two (19) is about one-third of one standard deviation, which is not much at all. To be more accurate, we’d find the standard deviation of all relief pitcher seasons. My math monkey is on spring break, so we’ll just use the ST DEV of their individual seasons.

If you’re interested in milestones, Billy Wagner has never had an ERA+ reach 300 or beyond, but Rivera has done so twice — twice in the last four seasons. In fact, they were his age 35 and 38 seasons. I thought the guy was supposed to get old and fizzle away. Wagner has had a 200 or greater ERA+ three times; Rivera has done so nine times including those two 300+ ERA+ seasons.

The point of the comparison was really just to ascertain some entertainment value. Both pitchers are first-ballot Hall of Famers and, if and when Wagner becomes healthy again, any team would kill to have either of them at the back of the bullpen.

Could Brad Lidge join the conversation? Sure, he just has to put up a string of dominant seasons starting with his age 32 season in 2009 and it has to continue for a good six or seven years. When analysts say that relief pitchers are fickle and you really don’t know what you’re getting year-to-year, they are certainly not talking about Billy Wagner or Mariano Rivera.